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Date: Wed, 15 Apr 2015 09:22:37 -0400
From: Sasha Levin <sasha.levin@...cle.com>
To: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
CC: Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Guilherme Cox <cox@...puter.org>,
Tony Luck <tony.luck@...il.com>,
Xie XiuQi <xiexiuqi@...wei.com>
Subject: Re: [PATCH 07/18 v3] tracing: Add TRACE_DEFINE_ENUM() macro to map
enums to their values
On 04/02/2015 09:38 PM, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
>
> Several tracepoints use the helper functions __print_symbolic() or
> __print_flags() and pass in enums that do the mapping between the
> binary data stored and the value to print. This works well for reading
> the ASCII trace files, but when the data is read via userspace tools
> such as perf and trace-cmd, the conversion of the binary value to a
> human string format is lost if an enum is used, as userspace does not
> have access to what the ENUM is.
>
> For example, the tracepoint trace_tlb_flush() has:
>
> __print_symbolic(REC->reason,
> { TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" },
> { TLB_REMOTE_SHOOTDOWN, "remote shootdown" },
> { TLB_LOCAL_SHOOTDOWN, "local shootdown" },
> { TLB_LOCAL_MM_SHOOTDOWN, "local mm shootdown" })
>
> Which maps the enum values to the strings they represent. But perf and
> trace-cmd do no know what value TLB_LOCAL_MM_SHOOTDOWN is, and would
> not be able to map it.
>
> With TRACE_DEFINE_ENUM(), developers can place these in the event header
> files and ftrace will convert the enums to their values:
>
> By adding:
>
> TRACE_DEFINE_ENUM(TLB_FLUSH_ON_TASK_SWITCH);
> TRACE_DEFINE_ENUM(TLB_REMOTE_SHOOTDOWN);
> TRACE_DEFINE_ENUM(TLB_LOCAL_SHOOTDOWN);
> TRACE_DEFINE_ENUM(TLB_LOCAL_MM_SHOOTDOWN);
>
> $ cat /sys/kernel/debug/tracing/events/tlb/tlb_flush/format
> [...]
> __print_symbolic(REC->reason,
> { 0, "flush on task switch" },
> { 1, "remote shootdown" },
> { 2, "local shootdown" },
> { 3, "local mm shootdown" })
>
> The above is what userspace expects to see, and tools do not need to
> be modified to parse them.
>
> Cc: Guilherme Cox <cox@...puter.org>
> Cc: Tony Luck <tony.luck@...il.com>
> Cc: Xie XiuQi <xiexiuqi@...wei.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
Hey Steven,
I'm seeing the following when booting:
[ 10.678876] BUG: KASan: out of bounds access in trace_event_enum_update+0xb1d/0xb70 at addr ffffffffa6c4dc68
[ 10.680222] Read of size 1 by task swapper/0/1
[ 10.680222] Address belongs to variable print_fmt_9p_client_req+0x848/0x880
[ 10.680222] CPU: 19 PID: 1 Comm: swapper/0 Not tainted 4.0.0-next-20150415-sasha-00064-g7858a62 #2147
[ 10.680222] ffffffffa6c4dc68 00000000915e69dc ffff88004e8efb18 ffffffffa1b4f7a6
[ 10.680222] 0000000000000000 ffff88004e8efba8 ffff88004e8efb98 ffffffff976544b1
[ 10.680222] ffff88004e8efbd8 ffffffff990134a4 0000000000000282 ffffffffa444e381
[ 10.680222] Call Trace:
[ 10.680222] dump_stack (lib/dump_stack.c:52)
[ 10.680222] kasan_report_error (mm/kasan/report.c:132 mm/kasan/report.c:193)
[ 10.680222] ? snprintf (lib/vsprintf.c:2069)
[ 10.680222] ? vsprintf (lib/vsprintf.c:2069)
[ 10.680222] ? trace_event_enum_update (kernel/trace/trace_events.c:1807)
[ 10.680222] __asan_report_load1_noabort (mm/kasan/report.c:230 mm/kasan/report.c:248)
[ 10.680222] ? trace_event_enum_update (kernel/trace/trace_events.c:1807)
[ 10.680222] trace_event_enum_update (kernel/trace/trace_events.c:1807)
[ 10.680222] tracer_init_tracefs (kernel/trace/trace.c:4122 kernel/trace/trace.c:6750 kernel/trace/trace.c:6848)
[ 10.680222] ? clear_boot_tracer (kernel/trace/trace.c:6825)
[ 10.680222] ? clear_boot_tracer (kernel/trace/trace.c:6825)
[ 10.680222] do_one_initcall (init/main.c:788)
[ 10.680222] ? try_to_run_init_process (init/main.c:777)
[ 10.680222] ? parse_args (kernel/params.c:131 kernel/params.c:216)
[ 10.680222] ? trace_hardirqs_on (kernel/locking/lockdep.c:2630)
[ 10.680222] kernel_init_freeable (init/main.c:853 init/main.c:861 init/main.c:880 init/main.c:1001)
[ 10.680222] ? local_clock (kernel/sched/clock.c:392)
[ 10.680222] ? start_kernel (init/main.c:973)
[ 10.680222] ? finish_task_switch (kernel/sched/core.c:2249)
[ 10.680222] ? finish_task_switch (include/linux/tick.h:186 kernel/sched/core.c:2263)
[ 10.680222] ? finish_task_switch (kernel/sched/sched.h:1077 kernel/sched/core.c:2245)
[ 10.680222] ? rest_init (init/main.c:928)
[ 10.680222] kernel_init (init/main.c:933)
[ 10.680222] ? rest_init (init/main.c:928)
[ 10.680222] ret_from_fork (arch/x86/kernel/entry_64.S:631)
[ 10.680222] ? rest_init (init/main.c:928)
[ 10.680222] Memory state around the buggy address:
[ 10.680222] ffffffffa6c4db00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 10.680222] ffffffffa6c4db80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 10.680222] >ffffffffa6c4dc00: 00 00 00 00 00 00 00 00 00 00 00 00 00 fa fa fa
[ 10.680222] ^
[ 10.680222] ffffffffa6c4dc80: fa fa fa fa 00 00 00 00 fa fa fa fa 00 00 00 00
[ 10.680222] ffffffffa6c4dd00: fa fa fa fa 00 00 00 00 fa fa fa fa 00 00 00 00
Thanks,
Sasha
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